Aluminothermic reduction mixtures

ABSTRACT

An aluminothermic reduction mixture includes aluminum powder and iron oxide formed of ferric oxide (Fe 2 O 3 ) particles with a special shape and other constituent parts.

BACKGROUND OF THE INVENTION

[0001] The invention relates to an improvement in aluminothermic reduction mixtures used to join the ends of steel rails. The improvement is directed to the use of a special type of iron oxide in the mixture.

FIELD OF THE INVENTION

[0002] At the end of the 19th century an aluminothermic process (the THERMIT® process) was developed and has provided a strong and efficient way to join rail ends together in the field and has led to the development of continuous welded rail.

[0003] While the THERMIT® process has had various applications over the years, at the present time it is used primarily to weld rail ends together.

[0004] The aluminothermic reduction of iron oxides to produce ferroalloys originally employed mill scale obtained as a byproduct of various hot working operations in steel plants. The mill scale has the form of flat platelets and when obtained from a steel plant is usually wet, may contain foreign materials and has a relatively low oxygen content. Accordingly, raw mill scale must be processed before it can be used in an aluminothermic reduction mixture. Note FIG. 1b of the drawing showing roasted oxide processed for use in the THERMIT® process.

[0005] In one approach, the raw mill scale is simply dried and sieved in a suitable apparatus. Such a procedure does not alter the oxygen content of the mill scale.

[0006] Raw mill scale obtained from a pipe mill contains small pieces of steel resulting from the pipe-threading operation. These pieces of steel can become segregated in less dense iron oxide and produce erratic results. Subsequent drying and sieving does not overcome the problem.

[0007] In another approach, the raw mill scale is processed in an oxide-roasting kiln. In an oxidizing atmosphere at high temperatures, the oxygen content is increased and small metal fragments become completely converted to additional oxide. Such procedure has problems including the high investment cost for the kiln and the round-the-clock operation which is costly.

[0008] The prior art includes a disclosure of the use of spherical iron oxide in place of part of the roasted mill scale. Note U.S. Pat. No. 5,370,726 where the spherical iron oxide is utilized to counteract the tendency of conventional mixtures to segregate during transport and handling. In this U.S. patent, spherical particles are screened to a desired particle size range of 0.1 to 2 mm. According to the patent, the course of the metallothermic reaction mixture is stabilized and demixing during transport, handling and storage is reliably avoided. Note FIG. 1C of the drawing illustrating the spherical particles in a range of sizes.

[0009] In other prior art it has been known to use pellets in the aluminothermic mixtures, however, the consistency of the resultant weld has been a problem. Over the past century, efforts have been made to provide aluminothermic mixtures yielding a consistent, reproducible weld.

SUMMARY OF THE INVENTION

[0010] In a continued effort to better the aluminothermic reduction mixture and improve the welds for joining rail ends, consideration has been given to improve the reliability, consistency and cost of forming the welds. Due to the past experience with the flat platelets of mill scale and spherical particles for counteracting segregation of the mixture, consideration was given to increasing the surface area of the ferrous oxide particles.

[0011] Accordingly, a source of iron oxide was found where the individual particles had a prism-like shape, not true prisms according to the dictionary definition, but with shapes significantly different from flat platelets and spherical particles. The prism-like particles are generally elongated in one direction with sides extending in the elongated direction and ends extending transversely of the elongated direction and contacting the edges of the sides.

[0012] In the course of experimentation, it was found that the prism-like particles in a size range of minus 20 mesh to plus 200 mesh afforded optimum welds superior to welds formed with mill scale or a mixture of mill scale and spherical particles.

[0013] The prism-like particles did not require any expensive processing, but were formed from hematite ore (ferric oxide—Fe₂O₃), which was placed in the desired form after mining by crushing, drying and screening.

[0014] The prism-like particles are available from Integral Solids and Solutions of Ramsey, N.J., and are designated internally by the assignee, Orgo-Thermit, Inc., as KO₂O₃ oxides.

[0015] Surprisingly, the reaction was found to be more energetic than when conventional oxides are used so that the normal additions of steel could be increased without impairing weld quality. It is more economical to obtain iron units by melting steel additions than to generate them from the reaction of iron oxides with expensive aluminum.

[0016] Further, it was also surprising to find that unusually more consistent results were gained when the novel oxide was used. In a random sampling of 20 welds made with the new mixture and 20 welds made with the roasted mill scale mixture it was found that more consistent results were obtained with the new oxide mixture, as judged by the aluminum content of the welds.

BRIEF DESCRIPTION OF THE DRAWING

[0017] The drawing is made up of three black and white photographs illustrating enlargements in the range of approximately 20 magnifications of the iron oxide particles.

[0018]FIG. 1a shows the assignee's KO₂O₃ oxide embodying the invention;

[0019]FIG. 1b shows the prior art roasted oxide; and

[0020]FIG. 1c shows the prior art spherical oxide.

DETAILED DESCRIPTION OF THE INVENTION

[0021] The aluminothermic-reaction mixture embodying the invention comprises aluminum powder and an iron oxide substantially all of which is ferric oxide (Fe₂O₃) or (KO₂O₃) in the form of prism-like particles as described above ranging in size from minus 20 mesh to plus 200 mesh or approximately 0.033″ to 0.003″. As can be seen in the photograph of FIG. 1a, the ferric oxide (Fe₂O₃) is formed of a plurality of particles of different sizes. The particles are elongated in one direction and have a prism-like configuration though not true prisms. Generally, the particles have a four-sided configuration through they are not limited to such a shape. When used in aluminothermic rail welding mixtures, the cold metal addition can be increased for economic benefits and the reactions are unusually consistent. The cold metal addition can be a variety of small steel particles, such as punchings and nail beards representing disposable particles resulting from steel processing operations.

[0022] The composition of the aluminothermic reaction mixture depends on the spacing between the rail ends to be welded. The following are examples of the compositions of the mixtures for 1″ and 3″ spacings between the rail ends. 1″ Weld INGREDIENTS % Aluminum powder 18.0 Cold metal additions 6.1 FeMn C alloy 18.4 Sand 0.3 FeV alloy 0.5 Ferric oxide 56.7 (Fe₂O₃) (KO₂O₃)

[0023] 3″ Weld INGREDIENTS % Aluminum powder 17.3 Cold metal additions 11.2 FeMn C alloy 16.4 Sand 0.3 FeV alloy 0.4 Ferric oxide 54.3 (Fe₂O₃) (KO₂O₃)

[0024] Depending on the dimension of the welds between the rail ends, the percentages of the aluminum powder and the ferric oxide is varied with aluminum powder in the range of 16% to 19% and ferric oxide (Fe₂O₃) in the range of 53% to 58%.

[0025] The ferric oxide is available in large quantities and in ready-to-use condition. It does not need any conditioning equipment requiring a capital investment such as an oxide roasting kiln. Further, there are no operating costs for preparation of the ferric oxide. Moreover, there is no requirement for maintaining a large inventory of the ferric oxide as compared to the use of raw mill scale and roasted oxide; that is, the ferric oxide, ready to be used, can be loaded into the production silo on the day a shipment arrives. 

What is claimed is:
 1. Aluminothermic reduction mixture comprising aluminum powder and iron oxide with the iron oxide comprised of substantially all ferric oxide (Fe₂O₃) formed of prism-like particles in a size range of minus 20 mesh to plus 200 mesh.
 2. Aluminothermic reduction mixture, as set forth in claim 1, wherein said mixture includes at least one additional constituent.
 3. Aluminothermic reduction mixture, as set forth in claim 1, wherein said prism-like particles are generally elongated in one direction, with generally planar sides extending in the elongated direction with said sides meeting along edges extending in the elongated direction and with ends extending transversally of the elongated direction and contacting said sides.
 4. Aluminothermic reduction mixture, as set forth in claim 2, wherein said mixture comprises at least three constituents.
 5. Aluminothermic reduction mixture, as set forth in claim 2, wherein based on 100% of said mixture said aluminum powder is in the range of 16% to 19%, and the ferric oxide (Fe₂O₃) is in the range 53% to 58%.
 6. Aluminothermic reduction mixture, as set forth in claim 4, wherein said constituents includes steel particles, FeMn C alloy, sand and a FeV alloy.
 7. Aluminothermic reduction mixture, as set forth in claim 6, wherein based on 100% of said mixture, said aluminum powder is in the range of 16% to 19%, said ferric oxide (Fe₂O₃) is in the range of 53% to 58%, said steel particles are in the range of 5% to 12%, said FeMn C is in the range of 15% to 19%, sand is in the range of 0.2% to 0.4% and FeV alloy is in the range of 0.3% to 0.6%.
 8. Aluminothermic reduction mixture, as set forth in claim 6, wherein said steel particles are one of steel nail beards and steel punchings. 